|Application of Florel to petunias releases the plants’ lateral branches from apical dominance without removal or injury to the shoot apex.Greenhouse operators have access to an expanding number of plant growth regulators that can be profitably used to manipulate crop growth and development. Among the oldest of this group of products is Florel, which remains one of the most versatile growth regulators.
Much has been written about ethylene’s place in the commercial greenhouse. While most growers have learned that ethylene is the last hormone they want present in a postharvest setting because of its negative effects including hastening flower senescence, research has provided them with a very different understanding of ethylene’s role during plant production.
A subtle shift has taken place from describing Florel as a chemical pinching agent to a more accurate lateral branching agent. This change has been made because Florel does not kill the stem growing tip. Rather, it stimulates lateral branching below the tip resulting in the release from apical dominance.
The traditional practice of manual pinching also results in the development of lateral branches. However, a plant’s branching potential is limited because the shoot is not allowed to continue growing. Continued growth results in new nodes from which additional branching occurs.
When Florel is applied, because the growing tip continues to grow, additional nodes and subsequent branches develop resulting in more branching than hand pinching generates. This multiple branching is desirable for both vegetative stock plants, as well as for many finished crops.
As Florel applications increasingly replaced manual pinching for many crops, it began to be described as a chemical pinching agent. More accurately, it should be described as a branching stimulator.
Ethylene and plant breeding
Advances in plant breeding have made progress in the area of natural branching. Today’s new cultivars branch more freely than previous releases. As breeders focus on the selection criterion of free branching they are, in effect, selecting against apical dominance, one of ethylene’s effects on growth. This may cause some to wonder if breeders are also affecting other plant functions that this hormone influences during a plant’s life cycle.
Florel is also an inhibitor of internode elongation and inhibitor of flowering. It is among a select few products that has uses during every stage of production, including stock plant culture, cutting propagation, young plant development and finished crop growth.
Growth regulator vs. plant hormone
Most traditional growth regulators are not plant hormones but, instead, chemicals that have an effect on a plant’s naturally produced hormones. Growth regulator products that are designed to control excessive growth by inhibiting internode elongation usually work on the plant’s internally produced gibberellins. By either interfering with the chemical pathways that synthesize these hormones or by preventing gibberellins from carrying out their normal functions once they are synthesized, growth regulators control stem elongation which can result in higher quality plants and more profitable crops.
The most commonly used non-hormone based growth regulators are A-Rest, Cycocel, B-Nine, Bonzi and Sumagic. Recently, the active ingredients of Bonzi and Sumagic became off-patent chemicals which has resulted in the commercial release of several additional products.
Florel has been used for agricultural purposes for about 50 years. Its active ingredient, ethephon, is a molecule that releases ethylene under the right conditions. When a Florel foliar spray is applied, as ethephon penetrates into the plant’s leaf, stem and flower tissue the surrounding pH increases relative to that of the spray solution. This pH rise triggers the ethephon molecule to break apart, releasing ethylene inside the tissue. Application of Florel delivers a naturally-occurring, gaseous hormone into plants in controlled, liquid doses high enough to have beneficial effects yet low enough to avoid ethylene’s detrimental effects. Commonly applied concentrations of Florel range from 100-500 parts per million.
Fascination, a more recently available growth regulator, is a mixture of two plant hormones, cytokinin and gibberillin. Cytokinins are known to stimulate cell division and increase branching in plants. Gibberillins are used to stimulate cell elongation causing short plants to grow taller, faster. Gibberillins also are being used to expand poinsettia bracts. The combination of the two hormones in this product is yielding better results than using either hormone alone.
The five basic plant hormone groups are auxins, gibberillins, cytokins, ethylene and abscisic acid. Agronomists and horticulturists have made impressive progress in learning how to manipulate crop development through the use of these hormones to improve yields, quality and profit. Inside the plant, all five hormone groups are present simultaneously and are intimately associated with each other. I encourage growers to learn about these individual hormones, and how they affect plant growth and to keep up with the rapidly expanding knowledge base on them.
Future growth control products, like Fascination, will blend other hormones as their interactions are better understood. One such blend that I think would have much potential is gibberellin mixed with Florel. For stock plants and late season flower control of finished plants, Florel would control flowering and the gibberellin would overcome inhibition of internode elongation caused by the ethylene.
Peter Konjoian is president, Konjoian’s Floriculture Education Services Inc., (978) 683-0692; firstname.lastname@example.org.